In recent years, optical filters that sufficiently transmit light in a visible wavelength range but shields light in a near-infrared wavelength range have been used for various applications.
For example, in an imaging device such as a digital still camera and a digital video camera, a solid-state image sensor (CCD, CMOS, the like) is used. In order to make sensitivity of the solid-state image sensor close to visibility of a human being, an optical filter is disposed between an imaging lens and the solid-state image sensor.
Among these, as an optical filter for an imaging device, near-infrared absorbing glass in which CuO or the like is added to fluorophosphate-based glass or phosphate-based glass so that light in the near-infrared wavelength range is selectively absorbed, and a glass filter using the same have been known (see Patent Reference JP-B 4169545). However, in the light-absorbing glass filter, performance to shield light with wavelengths in the near-infrared range and a transmitting property for a wavelength band (630 nm to 700 nm) which is required for photographing a dark part more brightly are not sufficient. In addition, due to layer formation restriction to prevent a function of the solid-state image sensor from being obstructed, an optical filter having a sufficient near-infrared cut filter function has not been obtained in the present circumstances.
Therefore, in order to solve the above problems, there have been developed a reflection-type interference filter in which, for example, a silicon oxide (SiO2) layer and a titanium oxide (TiO2) layer are stacked alternately on a substrate and which reflects and shields light in the near-infrared wavelength range by the interference of light, a film in which a dye that absorbs light in the near-infrared wavelength range is contained in a transparent resin, and the like (see Patent Reference JP-A 2008-181028). There has also been developed an optical filter being the combination of these, in which a resin layer containing a dye that absorbs near-infrared light and a layer that reflects near-infrared light are stacked (see Patent Reference JP-A 2008-051985). Further, a resin layer containing a dye that absorbs near-infrared light is known to public, for instance (see Patent Reference JP-A 2012-008532).